1. Field of the Invention
The present invention relates to an electrical device for stackably interconnecting two integrated circuit packages and commoning corresponding package leads.
2. Prior Art
There are many instances where it is desirable to interconnect corresponding leads of integrated circuit packages and more importantly to stack the packages thereby saving printed circuit board space. Some instances call for stacking integrated circuit packages to increase the memory cabilities while others call for combining various integrated circuit packages, such as a microprocessor package and a memory unit.
Integrated circuit packages are packaged in leadless and leaded configuration. A leadless integrated circuit package contains no leads but rather contains conductive pads on the edges of the chip substrate for interconnection to a stackable conductor. An example of a stackable interconnection for leadless integrated circuit packages can be found in U.S. Pat. No. 4,018,494. A lead frame approach can be used for interconnecting components with a leadless integrated circuit package, see U.S. Pat. No. 4,142,287. On the other hand, integrated circuit packages can be leaded, having leads projecting outwardly from the circuit substrate. It is the latter leaded configuration to which the subject invention is addressed.
Leaded integrated circuit packages can be formed in various configurations but most importantly for this discussion, the typical configuration is the dual in-line package (DIP). The DIP comprises an integrated circuit interconnected to a lead frame, the integrated circuit being totally enclosed within a dielectric body; the leads being partially enclosed within the body.
The integrated circuit package body generally includes a top and bottom surface, and side and endwalls. The DIP has leads extending outwardly from the sidewalls then bending downwardly. The leads are placed in opposed parallel rows and typically range from 4-60 leads per package.
Other common configurations for integrated circuit packages include the SOIC, the SOJ and the square package, although each of these involve a plastic body having leads extending from the body. The SOIC, or gull-wing, has leads extending outwardly from the package sidewalls, the leads then bent outwardly to form feet parallel to the top and bottom surface and parallel to the printed circuit board to which they are mounted. The SOJ packages have leads extending outwardly from the sidewalls but the leads are then formed under the package body, the leads being formed in the shape of a "J". Square packages are integrated circuit packages having the plastic body formed in a square shape with leads extending from all four sides of the body.
Typical stacking arrangements for integrated circuit packages involve commoning the same respective leads on stacked packages, that is, when stacking two 8-pin DIPs, pin 1 on the first DIP would be commoned with pin 1 of the second DIP, and so on through pin 8. Conditions do exist however where a lead on the upper package must be commoned to a lead on the opposite side of the lowor package, thus complicating the interconnection. Using the same 8-pin example above, pin 3 on the top DIP would be commoned to pin 6 on the lower DIP.
Another problem with presently available designs for stacking DIP connectors is that terminals within the connectors are individually formed and placed in their respective socket housing, creating manufacturing and handling difficulties. Several designs of connectors are presently available utilizing the individually formed terminals, for example, see U.S. Pat. Nos. 4,080,026; 4,312,555; 4,406,508; 4,116,519; 4,192,565; and 4,356,532.
It can be appreciated then that a connector designed such that the terminals are formed in carrier strip or lead frame configuration with the socket housing molded around the terminals, would be a significant advance in the technology, requiring much less cost for maufacturing. At least one design presently exists where the terminals are formed in a lead frame configuration, see for example U.S. Pat. No. 4,364,620.
As best shown in FIGS. 10 and 12 of the '620 patent, the terminals are initially formed in a lead frame configuration. The housing is not formed around the lead frame but rather the lead frame is bent around lines 150 of FIG. 10, producing a configuration having an end view as shown in FIG. 1 and then inserted in the housing. The bending process precludes the possibility of commoning leads on the opposite sides of the upper and lower DIPs, as in the bent configuration of FIG. 11, terminals 88 and 136 are separated further apart than in the lead frame configuration. As the lead 88 and 136 are further spread after the bending operation, they could not possibly be connected to each other.